Manganese-zinc ferrite materials

ABSTRACT

A MANGANESE-ZINC FERRITE IS PROVIDED HAVING A BASIC COMPOSITION 30 TO 38% MNO, 51 TO 57% FE2O3 AND THE BALANCE ESSENTIALLY ZNO, THE COMPOSITION FURTHER CONTAINING BY WEIGHT 0.0U TO 0.5% CO2O3, 0 TO 3.2% SNO2, 0 (PREFERABLY 0.005) TO 1.25% LI2O, 0.02 TO 0.5% CAO AND 0.005 TO 0.05% SIO2.

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ms s s United States Patent O 3,769,219 MAN GANESE-ZINC FERRITE MATERIALS Izuru Sugano, Yoshihiro Kenmoku, Tsuneo Akashi, Tetsujin Matsubara, and Taneaki Okuda, Tokyo, Japan, assignors to Nippon Electric Company Limited, Shlba Goehome, Tokyo, Japan Continuation-impart of application Ser. No. 34,968, May 6, 1970. This application Apr. 13, 1972, Ser. No. 243,596

Claims priority, application Japan, May 9, 1969, t4/36,367 The portion of the term of the patent subsequent to Mar. Z8, 1989, has been disclaimed Int. Cl. C04b 35 /38 U.S. Cl. 252-6259 4 Claims ABSTRACT OF THE DISCLOSURE A manganese-zinc ferrite is provided having as a basic composition 30 to 38% MnO, 51 to 57% Fe203 and the balance essentially ZnO, the composition further containing by weight 0.01 to 0.5% C0203, to 3.2% Sn02, 0 (preferably 0.005) to 1.25% Li2O, 0.02 to 0.5 CaO and 0.005 to 0.05% SiO2.

This application is a continuation-impart of U.S. application Ser. No. 34,968, filed May 6, 1970, now abandoned.

The present invention relates to manganese-zinc ferrite materials with greatly improved quality factors, hysteresis loss factors, and temperature coefficients of initial permeability.

STATE OF THE ART As publicly known, manganese-zinc ferrites have found extensive use as soft magnetic materials for communications use in the frequency band up to near 100 kHz. However, unmodified manganese-zinc ferrites consisting only of the basic ingredients of manganese, zinc and iron oxides exhibit unsatisfactory quality factors, hysteresis loss factors and other magnetic properties. In order to meet the diversied fields of use, improvements in magnetic properties have been attempted by incorporating various additive agents into the basic manganese-zinc ferrite compositions.

A typical example of such improvements is disclosed in U.S. Pat. No. 3,106,534 (British Pat. 923,991, German publication 1,123,253, Dutch Pat. 108,427, French Pat. 1,246,679) in which the quality factor and the hysteresis loss factor are markedly improved by incorporation of the combined additive agents calcium oxide (CaO) and silicon oxide (Si02).

The rapid progress of present-day communications equipment has emphasized a need for miniaturization and better performance of magnetic cores and improved stability of magnetic materials, in order to meet the demands for wider operating temperature ranges of such equipment, and the development of materials having a constant temperature coefficient of the initial permeability over a wide temperature range is intensely desired.

The heretofore developed magnetic materials have been found to be insuicient to meet these requirements. For instance, the previously mentioned manganese-zinc ferrite compositions containing the two additives CaO` and SiOg possessed better quality factor and hysteresis loss factor than had been obtained by that time, but, nevertheless, they have been outdated in the light of continuing demands for more excellent magnetic properties. Furthermore, they had a drawback in that the temperature range for securing a constant temperature coeficient of the initial permeability Was considerably restricted.

It has also been reported that the addition of cobalt ions to the manganese-zinc ferrite compositions is effec- Patented Oct. 30, 1973 tive for improving the temperature coeicient of the initial permeability. (In this connection, reference is made to British Pat. No. 1,092,009.) Cobalt incorporation is, however, still unsatisfactory for improvements of quality factor and hysteresis loss factor. In addition, it is difficult to obtain a desired and constant temperature coefficient over a wide temperature range by the incorporation of cobalt alone, and this may be attained only at the expense of degraded quality factor and increased hysteresis loss factor. These facts will be detailed later with reference to Table 1.

OBJECTS OF THE INVENTION The object of the invention is, therefore, to provide improved manganese-zinc ferrite materials having small quality factor (tan /n), low hysteresis loss factor (hw) and low and constant temperature coeicient of initial permeability over a wide temperature range.

The other object of this invention is to provide improved manganese-zinc ferrite materials having at least one of the following stated magnetic properties, to wit: a small quality factor (tan /n) less than 1.5 10`6, a low hysteresis loss factor (hm) less than 5 and a desired value between 0.3 X10*6 and 10X10-6 of constant temperature coefficient of initial permeability Aft/ (,ugoAT) in the temperature range of -20 C. to 80 C.

DETAILS OF THE INVENTION This invention is characterized by the combined addition of cobalt, tin, lithium, calcium and silicon into basic manganese-Zinc ferrite compositions. The amounts of these elements as oxides comprise 0.01 wt. percent Wt. percent, 0 wt. percent Sn023-2 wt. percent, 0 Wt. percent LZOOZS wt. percent, 0.02 wt. percent wt. percent and 0.005 wt. percentSiOgOS wt. percent, respectively, wt. percent being based on basic manganese-z'mc ferrites containing no additives. It is preferred that the SnOz content be at least about 0.01 wt. percent and Li2O be at least about 0.005 wt. percent. The effective compositions of basic manganese-zinc ferrites are 30.0 mol percent to 38.0 mol percent MnO, 51.0 mol percent to 57.0 mol percent Fe203 and the balance ZnO. By taking advantage of the presence of the live additives, it is possible to control the temperature coefficient of initial permeability Ap/ (frgoznT) of manganese-zinc ferrites from about 0.3 10*6 to 1.0 106 while maintaining a small quality factor and a low hysteresis loss factor. The quality factor and hysteresis loss factor may be lowered to below 1.5 10*6 and below 5 at 100 kHz.

The manganese-zinc ferrites of this invention desirably have the following compositions and additives:

With such ferrites, a quality factor below 0.8 106 and a hysteresis loss factor below 2.7 may be attained, while providing a desired value between 03x10--6 and 1.0 106 of the temperature coefficient of initial permeability, each value being measured at kHz.

I II

MnO 30-33 mol percent 33-36 mol percent. FczOa 52.054.0 percent 53.5-55.0 percent. ZnO Balance Balance. C0203 0.0l-0.2 wt. percent 0.05-0.28 wt. percent SnOz 0.5-1.4 Wt. percent 1.0-2.5 wt. percent. LizO..- 0.00, preerably 00005-006 Wt. 0.025-0.1 wt. percent.

percen CaO-.- 0.020.25 wt. percent 0.02-0.3 Wt. percent. SiOz 0005-003 wt. percent 0005-003 wt. percent.

It is to be noted that the quality factor and the hysteresis loss factor as set forth in this specification are 2 dened by the following equation:

where R-=effective resistance of core (n), L=inductance of coil (H),

n=initial permeability of core, ,ue-:effective permeability of core, V=effecting volume of core (cm), and I=measuring current (A).

The temperature coefficient of initial permeability A/.t/ (n202.AT) as set forth in the specification is defined as follows:

The temperature range of 20 C.-80 C. is divided into equal degrees centigrade intervals and the highest 4 and containing fixed amounts of C0203, CaO and Si02 and varying amounts of Sn02 and Li20;

FIG. 2 illustrates two families of contours indicating the values of hw and A/.t/n202.AT), respectively, for various proportions of Sn02 and Li20, measured from the same ferrite as FIG. 1;

FIGS. 3 and 4 are graphs similar to FIGS. l and 2, respectively, measured from manganese-zinc ferrites with another basic composition and another amount of C0203;

FIGS. 5 and 6 are graphs similar to FIGS. l and 2, respectively, measured from manganese-zinc ferrites of another basic composition and another amount of C0203;

FIGS. 7 and 8 are graphs similar to FIGS. l and 2, respectively, measured from manganese-zinc ferrites with still another basic composition and still another amount Of C0203;

FIGS. 9 and 10 are graphs similar to FIGS. l and 2, respectively, measured from manganese-zinc ferrites with still another basic composition and still another amount 0 of C0203;

FIG. 1l shows values of tan //r as a function of the proportions of CaO and SiO2 for manganese-zinc ferrites having the basic composition the same as in FIGS. 3 and 4 and containing fixed amounts of C0203, Sn02 and Li2O and varying amounts of CaO and SiO2; and

FIG. 12 shows contours of the values of h2o as a function of the proportions of CaO and SiO2 for the same ferrites as FIG. 1l.

Before describing the examples of the invention, the unsatisfactory results obtained by sole addition of cobalt will be described. Our experimental results are shown in Table 1, in which the values of quality factor (tan /n), hysteresis loss factor (hm), and temperature coefficient of initial permeability An/(n202AT) in the temperature range from minus 20 C. to plus 80 C. are listed for three different MnZn ferrites containing cobalt ions in varying amounts which are added in the form of C0203.

TABLE 1 Composition I Composition II Composition III A l/(moi-AT) A ll/(moz-AT) AlL/(moAT) tan /n6 (2080 C.) tan /p, (-20-80 C.) tan (20-80 C.) Magnetic properties X10- Hro 10 10a 1o X10- X 1o X10-0 Amount of C0203 addition (wt. percent):

Composition II: 36.0 mol percent Mn Composition III: 34.0 mol percent Mn and lowest temperatures in each interval are referred to as T2 and T2. With respect to each of the five intervals divided, the temperature coefficient of initial permeability of a sample is determined according to the equation All/(#20 20412020 C.

where ,w1-1, .222 and ,123. C. represent initial permeabilities at T1, T2 and 20 C., respectively. Among five values of temperature coefficients, maximum and minimum values are taken into account. An arithmetic mean of the two values is defined to be temperature coefficient of initial permeability of the sample. The deviation of temperature coefficient, which is indicated with the symbol i after a value of temperature coefficient in each table of this specification, signifies the difference between the mean value and the maximum or minimum value.

Now, the invention will be described more in detail referring to examples and drawings. In the drawings,

FIG. l shows to families of contours indicating values of tan /n and Art/MOZAT respectively for various proportions of SnO2 and Li2O, measured from manganese-zinc ferrites having a xed basic composition 9.5 mol percent Zn and 54.5 mol percent FezOa. 13.0 mol percent ZnO, and 53.0 mol percent FeaOa.

As will be seen from Table 1, a most favorable C0203 content for both tan /,u and hm by no means agrees with that for Aa/ (c222/1T), while the least values of tan /,L and h1@ that can be realized are substantially determined by the proportions of Fe203 and MnO, notably by the mol percent of MnO. On the other hand, the value of Aa/(,u202.AT) is substantially governed by the cobalt content. Therefore, it is almost impossible to vary the absolute value of An/ (,u.202.AT) which is in turn constant over a wide temperature range while keeping the excellent values /,u and hm, by way of sole incorporation of cobalt ions.

The effectiveness of this invention will be described in detail of the examples.

In Examples 1 through 5, the effect of the combined incorporation of Sn02 and Li20 will be examined and the optimum amounts thereof defined, for manganese-zinc ferrites having different basic compositions and containing suitably fixed amounts of C0203 and commonly fixed amounts of CaO and SiO2. In example 6, there will be shown that the effective amounts of C0202 addition vary with the basic manganese-zinc ferrite compositions and the effective range of C0203 content will be defined. In

5 Example 7, there will be indicated that both quality factor (tan /n) and hysteresis loss factor (hm) are improved by the combined addition of CaO and Si02 under the coexistence of the other additives Sn02, Li20 and C0203 and the ranges of the effective addition for each of CaO and Si02 will be defined.

All samples used in the examples of this invention were prepared by the usual method of manufacturing sintered ferrities as will be mentioned.

Iron oxide, manganese carbonate, and zinc oxide as the basic constituents and some or all of the additive agents, cobalt oxide, tin oxide, lithium carbonate, calcium oxide and silicon oxide were weighed to obtain predetermined compositions and proportions and mixed in a ball mill for 60 hours with alcohol as a dispersion medium. The mixtures were presintered at 800` C. in air for 4 hours, followed by press-molding and sintering at 1180 C. in a nitrogen atmosphere containing 0.4 percent by volume oxygen for 8 hours. It will be noted here that all the samples used in Examples 1 through 6 contain 0.06 wt. percent calcium oxide and 0.02 wt. percent silicon oxide, although this is not clearly mentioned in each example.

Example 1 Referring to FIGS. 1 and 2 which show the values of tan /n, hm and AM/(MOZAT) of manganese-zinc ferrites having a basic composition of 34.0 mol percent MnO, 12.55 mol percent Zn and 53.45 mol percent Fe203 and containing 0.25 wt. percent C0203 and varying amounts of Sn02 and Li20, in the ranges of 0-3.5 wt. percent and 0-0.125 wt. percent, respectively, each of the quality factor tan /p, the hysteresis loss factor hm and the initial permeability temperature coefficient An/,u232zAT is markedly improved by the combined incorporation of Sn02 and Li20 together with C0203, Ca0 and Si02. These figures reveal that new and improved manganese-zinc ferrite materials are successfully obtained having excellent properties heretofore not obtainable-that is, tan /n less than 1.5 X10-6, h1@ less than 5 and An/,u202.AT) of any desired value between 0.2Xl0-6 and 0.5X10-6, each as measured at 100 kHz, by the combined incorporation in the ranges of 0.9 wt. percent Sn0232 wt. percent and 0 Wt. percent Li0'2088 wt. percent.

Example 2 With reference to FIGS. 3 and 4 showing the values of tan /n, hm and An/(n202.AT) of manganese-zinc ferrites with a basic composition of 34.0 mol percent MnO, 12.00 mol percent ZnO and 54.00 mol percent Fe203 and containing 0.3 wt. percent C0203 and varying amounts of Sn02 and Li20, 0-3 wt. percent and 0-0.13 wt. percent respectively, it will be readily understood that the combined addition of C0203, Sn02, Li20, Ca0 and Si02 is equally quite effective for improvements of the quality factor, hysteresis loss factor and temperature coffcient of initial permeability, in spite of the fact that the proportion of Fe203 and ZnO in the basic composition is changed from that in the samples of Example 1.

As will be evident from these figures, we have succeeded in the preparation of manganese-zinc ferrite materials having better magnetic properties than have hitherto been obtainedthat is, tan /,u less than 1.5 X10-6, hm less than 5 and Apt/(MOAT) of any desired value between 0.3X-6 and 0.8X10-6, each measured at 100 kHz., in the ranges of 0.4 wt. percent Sn021.5 wt. percent and 0 wt. TLi200l wt. percent.

A further inspection of these figures will reveal that, provided the amounts of the additives be confined within the ranges of 0.88 wt. percent Sn02 1.16 wt. percent and 0.03 wt. percent Li S 0.053 wt. percent, manganese-zinc ferrite materials with markedly improved magnetic properties are provided which may meet all of the requirements in which tan /p. is less than 6 hm is less than 2.7, and in which A/l/(n202AT) can be provided at any desired value between 0.5X106 and 0.6X10-6, each as measured at 100 kHz.

Example 3 FIGS. 5 and 6 show the three magnetic properties of Mn-Zn ferrite samples having a basic composition of 34.0 mol percent MnO, 13.60 mol percent ZnO and 52.4 mol percent Fe203 and containing 0.4 wt. percent C0203 and varying amounts of Sn02 and Li20, 0-2.5 wt. percent and 0-0.13 wt. percent, respectively. A comparison of these figures with those of Examples 1 and 2 will readily demonstrate that the combined addition of C0203, Sn02, Li20, Ca0 and Si03 is extremely advantageous for simultaneous improvements of quality factor, hysteresis loss factor and temperature coeicent of initial permeability, irrespective of further change in the proportion of Fe203 and ZnO in the basic composition.

It will be seen from these figures that tan /p. is less than 1.5 X10-6, hm is less than 5 and that An/(u232AT) having any desired value between 0.5 X 10-6 and 0.7 X 10-6 can be obtained in the ranges of 0 wt. percent Sn02L6 wt. percent and 0 wt. percent Li200.11 Wt. percent.

Example 4 FIGS. 7 and 8 illustrate the values of tan /a, hm and Aa/ (,1/.202.AT) of Mn-Zn ferrite samples having a basic composition of 30.0 mol percent MnO, 16.5 mol percent ZnO and 53.5 mol percent Fe203 and containing 0.1 wt. percent C0203 and varying amounts of Sn02 and Li20, in the ranges of 0-3.0 wt. percent and 0-0.12 wt. percent, respectively. A comparison of these figures with those of Examples l, 2 and 3 readily reveals that the combined addition of C0203, Sn02, Li20, Ca0 and Si02 is extremely advantageous for improvements of the quality factor, the hysteresis loss factor and the temperature coefficient of initail permeability, even where there is a reduced proportion of MnO in the basic composition.

An inspection of these figures also demonstrates that tan /n is less than 1.5 X10-6, that is hm is less than 5 and An/(u202.AT) having any desired value between 0.5X l0-6 and 1.0X'1.0 106 can be attained in the amounts of 0.5 wt. percent Sn021.4 wt. percent and 0 wt. percent Li200-06 wt. percent.

Example 5 Referring to FIGS. 9 and l0 which show contours of the three magnetic properties of Mn-Zn ferrite samples having a basic composition of 38.0 mol percent Mn0, 9.20 mol percent ZnOl and 52.8 mol percent lFe203 and containing 0.5 wt. percent C0203 and varying amounts of Sn02 and Li20, in the ranges from 0 to 3.5 wt. percent and from 0 to 0.13 wt. percent, respectively, the cornbined addition of C0203, Sn02, Li2O, CaO and Si02 is effective for improvement of each of the quality factor, the hysteresis loss factor and the initial permeability temperat-ure coeicient, even where the MnO content in the basic composition is increased as compared with the sarnples of Examples 1 through 4.

As will be evident from these figures tan hioS and A/i/(n202-AT) having any desired value between 0.25X10*6 and 0.45X 10-6 can be obtained in the ranges of 1.4 wt. percent Sn0225 Wt. percent and 0.05 wt. percent Li20 0.l25 wt. percent.

A close inspection of these figures further reveals that, by confining the 'amounts of the two additives Sn02 and Li20 within the range of 1.83 wt. percent .Sn022.05 wt. percent and 0.073 wt. percent .Li20009 wt. percent, improved manganese-zinc ferrites can be obtained which may meet all of the requirements that tan /u` is less than 0.7Xl06 that hm is less than 2.5 and that An/(n232-AT) can be taken at any desired value between 0.3 l0"6 and 0.4X10-6, each as measured at 100 kHz.

It has been demonstrated in Examples 1 through 5 that both of quality factor and hysteresis loss factor can be markedly improved and at the same time Ait/(,020AT) can fbe Varied at will, by the addition of Sn02 and Li2O both in varying amounts, C0203 in suitably Ifixed amounts and CaO and S102 in fixed amounts and further that the amounts of addition of Sn02 and Li20 most effective for improvements of these magnetic properties vary with changes in the basic Mn-Zn ferrite compositions. From Example 1, it will be apparent that tan n at values less than 1.5 106 and hm at values less than 5 can be attained by incorporation of Sn02 in an amount not exceeding 3.2 wt. percent if the basic compositions and/or amounts of incorporation of the other additives are suitably selected. Example 3 also indicates that the similar properties can be obtained without the incorportation of Sn02. n the other hand, Example 5 shows that the incorporation of Li20 not exceeding 0.125 wt. percent brings about the abovementioned excellent properties if the other factors are determined in a suitable manner. However, Li20 can be decreased to zero for the same purpose if Sn02 is present in the ferrite, as will be apparent from Examples l to 4 and Nos. 1 to 4 of Table 2. Thus, the amounts of incorporation of Sn02 and Li20 should lbe restricted to the ranges of 0 wt. percent Sn023.2 wt. percent and 0 wt. percent Li200l25 wt. percent, respectively.

In order to ensure the reproducibility of Mn-Zn ferrites havingr desired values of the aforementioned magnetic properties, it is beneficial to have both SnO2 and Li20 present together with the other additives in the ferrites. In this respect, the amounts of Sn0'2 and Li20 ernployed are preferably at least about 0.01 wt. percent and at least about 0.005 wt. percent, respectively.

Sample Nos. 5 and 6 of Table 2 show the magnetic properties of Mn-Zn ferrite samples in which 0.01 wt. percent Sn02 and 0.005 wt. percent Li20 are both present.

TABLE 4 Weight percent p/p202-AT C0203 S1102 11120, X10 hlt) X1 0. 005 3. 5 0. 100 l. 9 12. 0 (1. 05:0. 8) 0. 01 3. 0 0. 075 1. 7 10. 0 (0. 910. 6) 0. 1 2. 5 0. 050 1. 5 7. 0 (0. 75:0. 3) 0. 3 2. 0 0. 075 1. 3 5. 0 (0. 65:0. 1) 0. 5 0. 5 0. 075 1. 45 5. O (0. 55:0. 06) 0. 5 1. 2 0. 100 1. 5 10. 0 (0. 35:0. 03) 0. 6 0. 5 0. 100 2. 5 20. 0 (0. 25:0. 03) 0. 6 1. 5 0. 152 3. 0 30. 0 (0. 15:. 0l)

Tables 3 and 4 indicate the fact that the temperature coeflicient of initial permeability can be controlled by varying the content of each of the additives C0203, Sn02 and Li20. As is evident from Table 3, deviation from the mean value of An/(p202AT) becomes considerably large (in excess of i of the mean value). Moreover, the other properties become degraded where a content of C0203 is below 0.01 Wt. percent. It will be noted that Table 4 shows that tan /n and hm each increases to more than 1.5 106 and 5, respectively, where the C0203 content exceeds 0.5 wt. percent. From this experi-mental fact, the lower and upper limits of the C0202 content effective for improvements of the magnetic properties have been determined as 0.01 and 0.5 wt. percent, respectively. Although the effective C0203 content varies with proportions of Fe203 and MnO in the basic composition, it is possible to obtain Mn-Zn ferrites having excellent values of quality factor and hysteresis loss factor and a constant temperature coefficient of initial permeability, provided that the amount of C0202 is in the range of 0.01 wt. percent C020305 wt. percent.

Example 7 FIGS. 11 and 12 illustrate, respectively, the values of tan /p and hm of Mn-Zn ferrite samples having a basic composition of 54.00 mol percent F0203, 34.0 mol per- TABLE 2 Basic composition., mol percent Additives, Weight percent Magnetic properties Example 6 cent MnO and 12.00 m01 percent Zn0 and containing This experiment has verified that the value of the temperature coefficient of initial permeability can be controlled by varying the contents of C0202, S1102 and Li20 in a Mn-Zn ferrite composition while maintaining the excellent values of tan /p and hm.

Table 3 lists the lvalues of tan /p., hw and An/ (,u2O2.AT) taken from Mn-Zn ferrite samples containing the specified amounts of C0203, Sn02 and Li20 and the fixed amounts of CaO and S102 and which have a basic composition of 54.0 mol percent Fe202, 30.0 mol percent MnO and 16.0 mol percent ZnO. Table 4 shows the similar values of Mn-Zn ferrites having a basic composition of 53.3 mol percent Fe202, 38.0 mol percent MnO and 8.7 mol percent ZnO and containing the specilied amounts of C0202, SnO and Li20 and the xed amounts of CaO and Si02.

TABLE 8 Weight percent p/pQAT tan (-20-80 C.) C0203 S1102 Liao X10' o X10` 0. 005 3. 0 0. 010 2. 2 15. 0 (0. 75:0. 50) 0. 005 3. 5 0. 020 2. 0 10. 0 0. 65:0. 30) O. 01 2. 5 0. 050 1. 5 5. 0 (0. 5:t0. 10) 0. 01 2. 0 0. O75 1. 5 4. 5 (0. 455:0. 07) 0. 1 1. 3 0. 050 1. 4 4. 0 (0. 305:0. 05) 0. 2 1. 0 0. 100 2. 0 9. 5 (0. 205:0. 03) 0. 4 0. 5 0. 125 2. 5 17. 0 (0. 105:0. 22)

0.3 wt. percent C0203, 1.2 kt. percent Sn02, 0.05 wt. pervcent Li2O and varying amounts of CaO and SiO2, in the ranges of 0-0.7 wt. percent and 0-0.08 wt. percent, respectively. Table 5 shows the values of Air/ (Moz-AT) of the same samples.

TABLE 5 Weight percent Ap/04202-AT) (-2080 C.) CaO S102 X10-5 Table reveals that the addition of CaO and Si02 has little eiect 0n the temperature coefficient of initial permeability. Although the deviation from the mean value of temperature coeficient becomes a little larger as the amounts of CaO and SiO2 are larger or lesser than 0.2 wt. percent, respectively, as shown in Table 5, the deviation cari be reduced by varying the amounts of one or more of the additives C0203, Sn02 and Li20. This variation, however, does not materially affect the values of tan //r and hm.

The addition of CaO and SiO2 is effective in the ranges of 0.02-0.55 wt. percent and 0.005-0.055 wt. percent, as mentioned above. However, the deviation of the temperature coeticient becomes considerably large if the CaO and Si02 contents exceed 0.5 wt. percent and 0.05 wt. percent, respectively. The eiective ranges of CaO and Si02 are thus defined as 0.02Ca00.5 and 0.005SiO2O.05, respectively.

In Examples 1 through 7 the effective ranges 0f the ve additives have been defined. As for the basic composition, Icompositions of 30.0 to 38.0 mol percent MnO, 51.0 to 57.0 mol percent Fe203 and the balance Zn0 are favorable. The compositions with the upper and lower limits of MnO have already been exemplied. Table 6 shows examples of the compositions having the upper and lower limits 0f F6203.

TAB LE 10 mol percent Fe202 and the balance ZnO and containing 0.05 to 0.28 wt. percent C0302, 1.0 to 2.5 wt. percent Sn02, 0.025 to 0.1 wt. percent Li20, 0.02 t0 0.3 wt. percent CaO and 0.005 to 0.03 wt. percent Si02.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

1. A manganese-zinc ferrite consisting essentially of a basic composition of to 38 mol percent MnO, 51 to 57 mol percent Fe203 and the balance ZnO and further containing by weight the additives 0.01 to 0.5% C0202, 0.01 to 3.2% Sn02, 0.005 to 0.125% Li20, 0.02 to 0.5% CaO and 0.005 to 0.05% Si02.

2. A manganese-zinc ferrite consisting essentially of a basic composition of 34 to 38 mol percent MnO, 52.3 t0 56 mol percent Fe203 and the balance ZnO and further containing by weight the additives 0.03 to 0.5% C0203, 0.5 to 2.1% S1102, 0.02 to 0.1% Li20, 0.025 to 0.18% CaO and 0.008 to 0.025% SiO2.

3. A manganese-zinc ferrite consisting essentially of a Basic composition, mol percent Additives, weight percent Magnetic properties tall /u (-20-80 C.)

MnO ZnO F6203 C0203 Sn02 LQO CaO SiOg 10 hlo X 10-1 30. 0 10. 0 51. 0 0. 5 3. 0 0. 1 0. 06 0. 02 l. 0 4 0. SiO. 05 30. 0 19. 0 51. 0 0. 5 3. 0 0. 1 0. 00 0. 04 1. 5 5 0. SiO. 07 36. 0 7. 0 57. 0 0. 02 2. 0 0. 06 0. 05 0. 02 1. 3 5 0. 5:l:0. 05 36. 0 7. 0 57. 0 0. 02 2. 0 0. 05 0. 1 0. 02 1. 0 3 0. 5:l:0. 07 36. 0 7. 0 57. 0 0. 02 2. 0 0. 06 0. 4 0. 02 1. 5 5 0. 5:l:0. 1

The extensive experiments of the inventors have shown that manganese-zinc ferrites with a basic composition of 34.0 to 38.0 m01 percent M110, 52.3 to 56.0 mol percent Fe203 and the balance ZnO and containing 0.03 to 0.5 wt. percent C0203, 0.5 t0 2.1 wt. percent SnO2, 0.02 to 0.1 wt. percent Li20, 0.025 to 0.18 wt. percent CaO and 0.008 to 0.025 wt. percent Si02 may have far superior magnetic properties. The values of tan /ft less than 0.8 106, hm less than 2.7 and Aa(,u202.AT) be tween 0.3 106 and 10X10-6 can be realized by suitably selecting a basic ferrite composition and amounts of the additives within the mentioned ranges. It has also been found experimentally than tan /n less than 1.5 10s, hm less than 5 and Aa(p202.AT) between 0.3X10-5 and 1.0 106 with the deviation less than 120% can be easily obtained with ferrites having a basic composition of 30.0 to 33.0 mol percent MnO, 52.0 to 54.0 mol percent Fe202 and the balance ZnO and containing 0.01 to 0.2 wt. percent C0203, 0.5 to 1.4 wt. percent Sn02, 0.00 (preferably 0.005) to 0.06 wt. percent Li20, 0.02 to 0.25 wt. percent CaO and 0.005 to 0.03 wt. percent Si02 or with the ferrites having a basic composition of 33.0 to 36.0 mol percent Mn0, 53.5 to 55.0

basic composition of 30 to 33 mol percent MnO, 52 to 54 m01 percent Fe203 and the balance ZnO and further containing by weight the additives 0.01 to 0.2% C0203, 0.5 to 1.4% Sn02, 0.005 to 0.06% Li20, 0.02 to 0.25% CaO and 0.005 to 0.03% Si02.

4. A manganese-zinc ferrite consisting essentially of a basic composition 0f 33 to 36 mol percent MnO, 53.5 to 55 mol percent Fe203 and the balance ZnO and further containing by weight the additives 0.05 to 0.28% C0202, 1.0 to 2.5% Sn02, 0.025 t0 0.1% Li20. 0.02 to 0.3% CaO and 0.005 to 0.03% Si02.

References Cited UNITED STATES PATENTS 3,652,416 3/ 1972 Sugano et al. 252-629 3,574,116 4/ 1971 Sugano et al. 252--62.9

OSCAR R. VERTIZ Primary Examiner I. COOPER, Assistant Examiner U.S. Cl. X.R. 

